Peelable PTFE sheaths and methods for manufacture of same

ABSTRACT

The present invention provides improved medical introducer devices which incorporate a single or multi-layer PTFE peelable sheath. Devices of the present invention are suitable for use in inserting an ancilliary medical device, e.g., a catheter, guide wire and the like, into a patient. Methods of the present invention also are disclosed which employ a precision sintering process in order to produce sheaths having excellent tear properties and optimal peelability.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to single and multi-layerpolytetrafluoroethylene (PTFE) peelable sheaths and methods formanufacturing and use of such sheaths. Sheaths of the present inventionare particularly suited for use as cannulas and other medical introducerdevices.

[0003] 2. Background

[0004] Splittable cannulas have been employed in various medical andsurgical procedures for inserting catheters, guide wires and the likeinto patients. A typical procedure provides for insertion of a dilatoror needle into the vasculature of a patient while encased within asplittable sheath. After insertion, the dilator or needle may be removedleaving the sheath protruding from the patient's vein. An ancillarymedical device, e.g., a diagnostic or therapeutic catheter or guidewire,is then threaded through the sheath into the patient. The encasingsheath is then longitudinally sheared and removed from the catheter orguide wire and the patient such as by applying opposing force to opposedwings or tabs of the introducer device. See e.g., U.S. Pat. Nos.5,334,157; 5,221,263; 5,141,497; 5,098,392; 4,772,266; and 4,243,050;and WO 97/14456 and WO 97/14468.

[0005] For ease in shearing and overall handling of the device, it isdesirable to employ a sheath of minimal thickness, e.g., thin-walled,having some degree of flexibility.

[0006] Notable disadvantages have been observed when using devices whichincorporate a “tear-away” or splittable sheath. For example, easy andnon-traumatic removal of the sheath is critical. It is possible that thesheath may not tear evenly or completely, thereby necessitatingadditional maneuvering and application of excessive force to the device.Excessive movement or force exerted upon the sheath is likely to causedamage to the vasculature of the patient. There is also the potential ofaccidentally dislodging the catheter from its inserted position whiletrying to remove the sheath.

[0007] Many design configurations and processes have been investigatedin an effort to overcome the various deficiencies observed in devices ofthe prior art which incorporate a peelable sheath.

[0008] For example, certain devices and methods were developed whichemployed a skiving process in order to produce peelable sheaths. Usingsuch a process, approximately one half of the wall thickness of thetubing material, e.g. a plastic, typically is cut away in a longitudinaldirection. In that way, a weak spot in the tubing wall is presentedwhere the tubing material can be peeled.

[0009] U.S. Pat. No. 4,306,562 (Cook) discloses a flexible, tear apartcannula which may be removed by pulling tabs on opposite sides of thecannula following insertion of a catheter or other device into the body.That patent reports that the cannula tears readily in a longitudinaldirection along the length of the structure because it comprisesmaterial having a longitudinal orientation, e.g.,polytetrafluoroethylene or other plastics. The longitudinal orientationis achieved using a standard extrusion process, and a slitting operationis used to create the tabs for pulling the cannula apart. See also U.S.Pat. No. 4,581,025 (Cook).

[0010] It has been shown, however, that the cannulas produced inaccordance with the Cook patents present certain limitations. Forexample, despite the fact that the tubing material has a longitudinalorientation, peelability still can be problematic. Additionally, certainadditives which are added to the preferred tubing material, TEFLON(TEFLON is a registered trademark of DuPont forpolytetrafluoroethylene), for X-ray visualization cause discolorationwhen the sheath is tipped by conventional thermal processes. Thus, theCook devices may only be produced in dark colors (e.g., gray and black)that hide such discoloration.

[0011] U.S. Pat. No. 5,318,542 describes another process for producing asplit cannula device having predetermined break lines which reportedlyprovides enhanced disassembly of the cannula. Predetermined break linesare produced by a non-metal-cutting shaping process, thereby enhancinguniformity of the predetermined break lines and reducing the forceneeded to disassemble the cannula. See also, U.S. Pat. No. 5,104,388.

SUMMARY OF THE INVENTION

[0012] There remains a need for improved medical introducer deviceswhich incorporate a peelable sheath to facilitate smooth entry of anancillary medical device into a patient, and easy and non-traumaticremoval of the sheath following insertion of the ancilliary medicaldevice.

[0013] It would be desirable to develop a multi-layer sheathconfiguration, e.g., an inner layer which permits visualization by X-rayor fluoroscopic procedures, and an outer layer that is resistant todiscoloration by thermal processes. Such a configuration would bedesirable in that the device could be produced in a variety of colorsincluding white, blue or any other thermally stable color.

[0014] It also would be highly desirable to develop methods for themanufacture which produce single and multi-layer peelable sheaths withsuperior tear properties. More specifically, it would be highlydesirable to develop methods for the manufacture of such sheaths whichdo not rely on mechanical skiving of the sheaths. We have found thatskiving does not always produce tubing with good peel properties,especially when using tubing materials such as polytetrafluoroethylene.

[0015] We have now produced medical introducer devices which incorporatea single or multi-layer polytetrafluoroethylenepeelable (PTFE) sheath.

[0016] Preferred sheaths of the invention are characterized in part bybeing readily splittable along their length (longitudinally) without useof any type of mechanical skiving, score lines or the like.

[0017] The invention is based in part on the discovery that by impartingan appropriate longitudinal peel strength to a PTFE sheath, the sheathcan be readily split as desired without the need for any type ofmechanical skiving along the sheath length. Preferred peel strengths toprovide such longitudinal splitting are disclosed below.

[0018] An appropriate peel strength is suitably imparted to a sheath bya controlled curing process, sometimes referred to herein as “precisionsintering”. Thus, temperature and cure times are selected to provide theappropriate peel strength. Optimal temperature and cure conditions willvary among specific cure systems. That is, cure conditions may vary withthe type of heat source (e.g. radiant or convective heating), residenceor exposure times of the PTFE sheath material to the heat source(s),size (e.g. French) of the sheath material being cured, and the like. Seethe examples which follow for exemplary suitable cure conditions for thedescribed systems. Suitable cure conditions for any particular heatingsystem and sheath material also can be readily determined empirically,i.e. a sheath material can be exposed to alternative cure conditionsuntil conditions are identified that provide a desired peel strength. Inother words, cure conditions can be applied, and the peel strength ofthe cured strength measured to determine if those conditions did in factprovide a targeted peel strength value. If the peel strength is notappropriate, the cure conditions are simply varied until a desired peelstrength is provided.

[0019] Sheaths of the invention are useful for medical deviceapplications, particularly for use in inserting an ancilliary medicaldevice, e.g., a catheter, guide wire and the like, into a patient.

[0020] PTFE sheaths of the invention suitably may be of single layer ormultiple layer constructions.

[0021] Preferred multi-layer devices afford significant advantages overthe devices of the prior art. In one preferred multi-layer sheath of theinvention, the outer layer comprises a thermally stable, colored pigmentwhile at least one of the inner layers of the sheath comprises adetectable component, e.g. a radiopaque material for externalvisualization by X-ray or fluoroscopic procedures.

[0022] Using such a multi-layer configuration, no discoloration of thesheath is observed following conventional thermal tipping processes.Thus, devices of the present invention may be produced in a variety ofcolors, e.g., white, blue or any other thermally stable color, withoutsacrificing the radiopaque feature of the device.

[0023] The present invention also provides methods for manufacturingsingle or multi-layer peelable sheaths for use as cannulas and othermedical introducer devices. Methods of the present invention incorporateextrusion followed by a precision sintering process as generallydiscussed above in order to achieve optimally cured tubing for use as apeelable sheath. Thus, there is no need to mechanically skive the wallof the tubing to present a weakened, predetermined break line.

[0024] Preferred methods for single layer sheath manufacture include:providing a preform PTFE material; extruding the PTFE material intotubing using conventional extrusion procedures; drying the tubing; andimparting a desired peel strength to the sheath that enables facilelongitudinal splitting of the sheath without any type of mechanicalskiving of the sheath. Precision sintering cure conditions are suitablyemployed to impart a desired peel strength. A detectable material may beadded to the preform PTFE material in an amount sufficient to facilitateexternal visualization. Preferably, the detectable material comprises aradiopaque material for visualization by X-ray or fluoroscopicprocedures.

[0025] Preferred methods for multiple layer sheath manufacture includethe following: providing a first PTFE material blend for forming theinner layer of the sheath; preparing a second PTFE material for formingthe outer layer of the sheath; combining the first and second PTFEmaterials blends into a two layer preform; extruding the two layerpreform into tubing using conventional extrusion procedures; drying thetubing; and imparting a desired peel strength to the sheath that enablesfacile longitudinal splitting of the sheath without any type ofmechanical skiving of the sheath. Precision sintering cure conditionsare suitably employed to impart a desired peel strength.

[0026] A number of inner layer preform materials may be provideddepending upon the number of inner layers desired, i.e. the multiplelayer sheath may have 2 or more layers, typically 2, 3, 4 or 5 totallayers. Again, a detectable material may be added to one of the preformmaterials in an amount sufficient to facilitate external visualization.Preferably, the detectable material comprises a radiopaque material forvisualization by X-ray or fluoroscopic procedures.

[0027] Additionally, different colored pigments may be added to each ofthe outer and inner layer preform blends. In that way, thoughinseparable, the layers may be visibly distinguished.

[0028] A hub unit is preferably attached to either the single layer ormultiple layer sheath on the sheath proximal end to facilitatessplitting of the sheath upon application of an effective shearing forcethereon. For example, preferred hub may have opposed outwardly extending“wing” portions that can be manipulated (e.g. downward or inwardpressure) to facilitate longitudinal splitting of the sheath.

[0029] The sheath is also preferably tipped at the distal end thereof,e.g., using conventional thermal tipping processes.

[0030] Methods of introducing an ancilliary medical device, e.g.,catheter or guidewire, using a device of the present invention generallyinclude: inserting a needle or dilator assembly into the bore of apeelable sheath constructed in accordance with the present invention;piercing and dilating the vasculature of the patient using such anassembly; withdrawing the needle or dilator assembly from the sheathcomponent of the device; inserting the catheter or guide wire throughthe bore of the sheath to the desired target location; applyingoutwardly cooperating forces to the hub unit, e.g., via attached wingportions, to axially shear the sheath; and removing the sheath from thevasculature of the patient.

[0031] Using methods of the present invention, single or multi-layerpeelable sheaths are provided that facilitate easy, non-traumaticremoval of the sheath following insertion of the ancilliary medicaldevice.

[0032] Other aspects of the invention are discussed infra.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033]FIG. 1 is a side view of a medical introducer device whichincorporates a single layer peelable sheath in a preferred embodiment ofthe present invention.

[0034]FIG. 2 is a side view of a medical introducer device whichincorporates a multi-layer peelable sheath in an alternate preferredembodiment of the present invention.

DETAILED DESCRIPTION

[0035] As discussed above, the present invention provides single andmulti-layer peelable sheaths for use in medical devices such as cannulasand other introducer devices. Introducer devices are routinely used in avariety of medical and surgical applications, e.g., for insertion of anancilliary medical device such as a catheter, guide wire into a patient.The present invention employs a precision sintering process in order toproduce sheaths having excellent tear properties and optimalpeelability.

[0036] Preferred sheaths of the invention will exhibit a peel strengthof at least about 0.6 lbs., more preferably at least about 0.70 lbs.,still more preferably at least about 0.80 lbs., 1.0 lbs., 1.2 lbs., 1.4lbs., 1.6 lbs., 1.8 lbs. or 2.0 lbs., with a maximum peel strength ofabout 2.8 or 3.0 lbs.

[0037] Further preferred is where the sheath exhibits a relativelynarrow standard deviation around a tested peel strength, such a standarddeviation of no more than about ±0.40 lbs of a specific value, morepreferably a standard deviation of no more than about ±0.30 lbs, 0.20lbs or 0.10 lbs of a specific tested value.

[0038] As discussed above, preferred peel strengths will vary withsheath size, with generally higher peel strengths preferred for largersheaths. More particularly, for a sheath having a size up to about 9French (typically about 2, 3, or 4 French up to about 8 or 8.5 French),preferred peel strengths will be from about 0.5 lbs. up to about 2.0lbs., more preferably 0.6 lbs to about 2.0 lbs. For a sheath having asize from about 9 to about 13 French, preferred peel strengths will befrom about 0.75 lbs. up to about 2.5 lbs., more preferably 1.0 lbs toabout 2.0 lbs. For a sheath having a size from about 14 to about 18French or greater, preferred peel strengths will be from about 1.0 lbs.up to about 3.0 lbs., more preferably 1.0 lbs to about 2.5 lbs.

[0039] Referring now to the Drawings, FIG. 1 shows a preferredembodiment of a medical introducer device 10 constructed in accordancewith the methods of the present invention. Device 10 comprises a singlelayer, peelable sheath 11 having a proximal end 12 and a tapered distalend 12′, and a bore 13 extending therebetween. (In accordance withconventional practice, “proximal end” designates herein the specifiedend closest to the medical personnel manipulating the introducer device,and “distal end” designates the specified end closest to the patient.)

[0040] Sheath 11 is formed from a polytetrafluoroethylene polymer (e.g.,TEFLON, registered trademark for polytetrafluoroethylene, commerciallyavailable from DuPont). Sheath 11 may further comprise materials such asfillers, colorants, and the like. Typical additional additives to thePTFE will be inorganic materials. It also will be possible, althoughtypically less preferred, to include additional organic materials,particularly high Tg polymers, with the PTFE.

[0041] As discussed above, sheath 11 preferably further comprises adetectable material, e.g., a radiopaque material, in an amountsufficient for external visualization by X-ray or fluoroscopicprocedures. Preferred radiopaque materials include barium sulfate,tungsten, bismuth sub-carbonate and bismuth trioxide. Preferably, theamount of radiopaque material present in the inner layer ranges fromabout 1% or 2% to about 12% by weight. Such a configuration permitsvisualization of the sheath within a patient by X-ray or fluoroscopicprocedures.

[0042] Referring now to FIG. 2, an alternate embodiment of a medicalintroducer device of the present invention is shown. Device 20,constructed in accordance with the methods of the present invention, isshown to include a multi-layer, peelable sheath 23 having a proximal end24 and a tapered distal end 24′, and a bore 25 extending therebetween.

[0043] Sheath 23 preferably includes a thermally stable outer layer 26and at least one inner layer 27. Preferably, both of these layers areformed from a flexible polymeric material, preferably apolytetrafluoroethylene polymer (e.g., TEFLON, registered trademark forpolytetrafluoroethylene, commercially available from DuPont).

[0044] In preferred embodiments of the present invention, outer layer 26further comprises a pigment that is not discolored by thermal processes.

[0045] In preferred embodiments of the present invention, inner layer 27further comprises a detectable material, e.g., a radiopaque material, inan amount sufficient for external visualization by X-ray or fluoroscopicprocedures. Preferred radiopaque materials include barium sulfate,tungsten, bismuth sub-carbonate and bismuth trioxide. Preferably, theamount of radiopaque material present in the inner layer ranges fromabout 1 or 2% to about 12% by weight. Such a configuration permitsvisualization of the sheath within a patient by X-ray or fluoroscopicprocedures.

[0046] In particularly preferred embodiments, inner layer 27additionally comprises a pigment (e.g., different in color from that ofthe outer layer) for visual distinction from outer layer 26.

[0047] Referring now to both FIGS. 1 and 2, devices of the presentinvention preferably further comprise a hub unit 14 attached, e.g.,molded, to the sheath at a proximal end thereof. The hub unit 14 iscapable of splitting the sheath upon application of an effectiveshearing force thereon.

[0048] Preferably, hub unit 14 is formed of polypropylene or othersuitable material. In preferred embodiments, hub unit 14 substantiallycircumscribes the proximal end of the respective sheath and comprises alongitudinal score or indentation 15 on opposing sides. In that way, thehub is in contact with a significant circumferential surface area at theproximal end of the respective sheaths and a defined break line ispresented for easy tearing of the sheath, e.g., along a longitudinalarea 16. Using such a configuration, the potential for the sheath totear unevenly or incompletely is avoided or at least significantlyreduced.

[0049] In preferred embodiments of the present invention, two or morewing portions 17 and 18 are attached, e.g., molded to the hub unit 14.Wing portions 17 and 18 preferably extend outwardly from the hub unit insubstantially diametrically opposed positions. Wing portions 17 and 18facilitate easy grasping with respect to hub unit 14 and effectiveshearing of sheath 11 and sheath 23.

[0050] It also is particularly preferred that the outer surfaces of wingportions 17 and 18 include topography to aid in manipulation and overallhandling of the introducer device. For example, as shown in theillustrative embodiments of FIGS. 1 and 2, preferably the exposed sidesof wing portions 17 and 18 have a plurality of raised gripping surfaces19.

[0051] In particularly preferred embodiments of the present invention,raised gripping surfaces 19 or other area(s) of wing portions 17 and 18are color-coded to designate particular sheath dimensions. This featureenables easy identification by attendant medical personnel of a desiredsheath size.

[0052] Sheaths 11 and 23 are typically adapted to snugly receive aconventional dilator assembly 20 or alternately, a needle assembly (notshown) in order to facilitate entry into a vein or artery of a patient.

[0053] Accordingly, in preferred embodiments of the present invention,wing portion 17 further comprises a locking lip 21 which secures flange22 of dilator assembly 20 or a comparable flange of a needle assembly.

[0054] Generally, distal end 28 of dilator assembly 20 extends beyondthe tapered distal end of the sheath in order to minimize trauma to thevasculature of the patient during the procedure.

[0055] Preferably, dilator assembly 20 is formed from a fluorinatedethylene-propylene resin. Other preferred fluorinated resins include,e.g., a tetrafluoroethylene polymer such as TEFLON (registered trademarkof DuPont for polytetrafluoroethylene).

[0056] Following dilation of the vasculature of the patient, dilatorassembly 20 is withdrawn and replaced with the desired ancilliarymedical device, e.g. catheter or guidewire. Upon application of force tothe hub unit 14 via wing portions 17 and 18, the sheath is peeled alonglongitudinal tear line 16 leaving only the ancilliary medical device inplace within the vasculature of the patient.

[0057] Suitable dimensions of the components of devices of the presentinvention can vary rather widely depending on the intended applicationand such dimensions can be readily determined by those skilled in theart based on the present disclosure.

[0058] Generally, dilator assembly 20 (or, alternately, a needleassembly) should have a diameter suitable for insertion into theselected vasculature of a patient. Sheath 11 and sheath 23 should have adiameter sufficient to accommodate such an assembly, and subsequently acatheter, guide wire or the like. Also, the diameters of the dilator aswell as the sheath for circumscribing the dilator will be greater thanthe corresponding diameters of a device that employs a percutaneousneedle rather than a dilator assembly.

[0059] For example, in particularly preferred embodiments of the presentinvention, peelable sheath 11 is about 5 to about 6 inches in length,denoted as x in FIG. 1. Preferably, dilator assembly 20 has a useablelength (length excluding luer threads or other connector at proximal end28) from about 7 inches to about 8 inches, denoted as y in FIG. 1.

[0060] Comparable dimensions, denoted by x′ and y′ in FIG. 2, aresuitably preferred for the multi-layer embodiment 20.

[0061] Other preferred dimensions for devices of the present inventionare shown in Table 1 below. TABLE 1 DILATOR SHEATH O.D. AVG FRENCH O.D.AVG. TIP I.D. MIN. (%/ I.D. SIZE (%/& .001) (+.002/−.000) &.001) MINWALL 4 F .052 .027 .076 .054 .008/.009 5 F .066 .037 .090 .068 .008/.0096 F .079 .037 .103 .081 .008/.009 7 F .092 .040 .118 .094 .009/.010 8 F.105 .040 .131 .107 .009/.010 9 F .118 .040 .144 .120 .009/.010 10 F.131 .040 .159 .133 .010/.011 10.5 F .137 .040 .165 .139 .010/.011 11 F.144 .040 .172 .146 .010/.011 12 F .157 .040 .185 .159 .010/.011 12.5 F.162 .040 .192 .164 .011/.012 13 F .170 .040 .200 .172 .011/.012 14 F.184 .040 .214 .186 .011/.012 15 F .196 .040 .227 .198 .011/.012 16 F.210 .040 .240 .212 .011/.012 18 F .236 .040 .266 .238 .011/.012

[0062] The present invention also provides methods of manufacturingsingle or multi-layer peelable sheaths for use in medical devices suchas cannulas and other introducer devices, e.g., sheaths for insertion ofa catheter, guide wire and the like into a patient. Methods of thepresent invention incorporate extrusion followed by a precisionsintering process in order to achieve optimally cured tubing for use asa peelable sheath. Thus, there is no need to mechanically skive the wallof the tubing to present a weakened, predetermined break line.

[0063] In the case of the multi-layer peelable sheath, methods of thepresent invention preferably also comprise adding different coloredpigments to each of the outer and inner layer preform blends. Generally,such pigments are added in amounts which are sufficient to produce thedesired colors. In that way, though inseparable, the layers may bevisibly distinguished.

[0064] The multi-layer configuration presents significant advantageswith respect to the devices of the prior art. In particular, we havediscovered that if the sheath consists of a co-extrusion (two or morelayers), it is possible to make any color sheath and that there is novisible discoloration of the external layer after thermal tipping. Thus,there is no need for devices of the present invention to be limited to anarrow range of colors (e.g., to dark colors only). Further, the abilityto produce sheaths in lighter colors has the added advantage of enablingone to visualize contaminants that may be present in the sheath.

[0065] Preferably, a hydrocarbon lubricant is added to the preformblends, and the preform blends are allowed to equilibrate for a periodof several hours prior to their combination in the case of themulti-layer sheath or prior to extrusion in the case of the single layersheath.

[0066] Sheaths of the present invention are produced using standardsingle or multi-layer polytetrafluoroethylene (PTFE) extrusionprocedures. For example, the two layer PTFE extrusion process istypically used to make fuel tubes with carbon-filled PTFE on the insideand natural PTFE on the outside. In utilizing this process, the presentinvention presents an improvement in terms of thermal resistance andcolor integrity of tubing.

[0067] As noted above, curing of the tubing is performed using aprecision sintering process, e.g., reduced sintering. We have discoveredthat reduced sintering provides single or multi-layer tubing withexcellent tear properties and optimal peelability. In contrast to theprior art, using the methods of the present invention, no skiving of thetubing is necessary to produce a peelable sheath.

[0068] Using the precision sintering process, the tubing is run througha series of temperature adjusted sintering ovens in order to producetubing which is not only cured to the desired degree but which also hasoptimal tear properties, e.g., tensile strength and elongation, as wellas peel strength.

[0069] Typically, the peel strength and other properties of the tubingare manually monitored at various intervals during the reduced sinteringprocess. Various temperature adjustments and sintering times may beemployed in order to produce tubing having the desired properties.However, the tubing is cured only until the desired peel strength isobtained.

[0070] Optimal peel strength will vary with tubing size. Referring toTable 2 below, target peel values are shown for various tubing sizes.TABLE 2 FRENCH PEEL STANDARD SIZE VALUE DEVIATION   4 F-8.5 F 0.85 +/−0.50 lbs.  9 F-13 F 1.25 +/− 0.50 lbs. 14 F-18 F 1.80 +/− 0.60 lbs.

[0071] In preferred embodiments of the present invention, methods ofmanufacture further comprise attaching, e.g., molding, a hub unit ontothe proximal end of the sheath which facilitates splitting of the sheathupon application of an effective shearing force thereon; attaching and aplurality of wing portions to opposing sides of the hub unit; andtipping the sheath at a distal end thereof, e.g., using conventionalthermal tipping processes.

[0072] The present invention also provides methods of introducing anancilliary medical device, e.g., catheter or guidewire, using a deviceof the present invention. Such methods generally include: inserting aneedle or dilator assembly into a peelable sheath constructed inaccordance with methods of the present invention; piercing and dilatingthe vasculature of the patient using such an assembly; withdrawing theneedle or dilator assembly from the sheath component of the device;inserting the catheter or guide wire through the bore of the sheath tothe desired target location; applying outwardly cooperating forces tothe hub unit, e.g., via attached wing portions, to axially shear thesheath; and removing the sheath from the vasculature of the patient.

[0073] The following non-limiting examples are illustrative of theinvention.

EXAMPLE 1

[0074] 25 lb. of PTFE fine powder (Teflon(® 6C, DuPont) was mixed with4.35 lb. of a hydrocarbon lubricant (Isopar® G, Exxon), 3.245 lb. of aradioopaque filler (67% Bi2O3 in Isopar G), 0.5 lb. of Gray pigmentconcentrate ( 67% gray pigment in Isopar G) and 0.25 lb. of blackpigment concentrate (67% black pigment in Isopar® G). (Final compositionis 7.8% Bi₂O₃, 1.2% gray, 0.6% black, based on total solids) Theseingredients were mixed in a Patterson-Kelly V-cone blender for 20minutes. This mix was then allowed to age for several hours toequilibrate.

[0075] The blend was made into a preform (2.5″ OD, 0.625″ ID). Theobject of preforming is to compact the blends in size and to make apreform that can be inserted into an extrusion machine. The preform wasplaced into an extrusion machine and extruded into tubing using a dieand mandril (0.2880″OD, 0.2650″ID). The tubing was run through a dryingoven to remove the hydrocarbon lubricant. The tubing was then runthrough 3 sintering ovens to cure the material. This tubing was then cutinto 8.25″ lengths.

[0076] The tubing produced had dimensions of 0.240″ OD×0.2170″ ID×8.25″long. The wall thickness was 0.0115″. The overall tube was black with ashiny surface.

[0077] Referring to Table 3 below, properties of the tubing produced inthis example are shown below as “Sample 2”. Data for Samples 1, 3 and 4are shown for purposes of comparison. TABLE 3 SAMPLE 1 SAMPLE 2 PRIORART PRESENT SAMPLE 3 SAMPLE 4 SAMPLE INVENTION UNDERCURE OVERCURE Dryingoven 1 (F) 400 400 400 400 Curing oven 1 (F) 840 720 700 1000 Curingoven 2 (F) 940 820 800 1080 Curing oven 3 (F) 1040 920 900 1180 MeltingPoint (C) 326.63 326.57 343.77 326.03 Width at Half 4.0 6.0 5.6 3.3Height (C) Tensile Strength 7083 6817 1333 5417 (PSI) Elongation (%) 288309 233 351 Peel strength (lb) 1.95 1.56 1.2 2.67 Peel Comments Unevenpeel, Straight, even Straight, even Uneven peel, partial peel peel peel.Lots of partial peel stringers.

[0078] Description of Samples:

[0079] Sample 1—This sample is presented for purposes of comparison. Itis a commercially available product comprising PTFE, and has a narrowmelting point peak at 327 degrees C. When split and peeled, it requireshigher peel force and does not peel smoothly. The tubing begins to peeland then one of the sections begins to narrow down and eventually endsbefore all of the tubing is split (partial peel).

[0080] Sample 2—This sample corresponds to a peelable productmanufactured in accordance with the methods of present invention. Thisproduct is not fully cured as indicated by the wider melting point peak.The tensile strength and elongation are similar to the fully curedproduct. However, the peel strength is reduced by 20% in relation to thefully cured product. The peel is straight and even so that the entiretubing is split.

[0081] Sample 3—This sample corresponds to a product that is almostcompletely uncured. This is visible by a melting peak at 344 degrees Cversus 327 degrees C for the other samples. This product is mottledwhite and black due to the undercure. The peel is straight and even,however, there are significant numbers of fibers that extend from thepeeled surface after peeling. This is unacceptable to the end user sincea piece may tear away and contaminate the area. In addition, thephysical properties are significantly reduced due to the lack of curingof the product.

[0082] Sample 4—This sample corresponds to a product that is curedharder than normal. This overcure is visible by the melting peak halfwidth. This product does not peel straight, similar to the fully curedproduct.

EXAMPLE 2

[0083] Blend 1—55.1 lb. of PTFE fine powder (Teflon® 6C, DuPont) wasmixed with 9.048 lb. of a hydrocarbon lubricant (Isopar® G, Exxon), and7.151 lb. of a radiopaque filler (67% Bi2O3 in Isopar G) (finalcomposition is 6.7% Bi₂O₃ based on total solids). These ingredients weremixed in a Patterson-Kelly V-cone blender for 20 minutes. This mix wasthen allowed to age for several hours to equilibrate.

[0084] Blend 2—55.1 lb. of PTFE fine powder (Teflon® 6C, DuPont) wasmixed with 10.379 lb. of a hydrocarbon lubricant (Isopar® G, Exxon), and0.573 lb. of a white pigment filler (67% white pigment in Isopar G).These ingredients were mixed in a Patterson-Kelly V-cone blender for 20minutes. This mix was then allowed to age for several hours toequilibrate.

[0085] The blends were made into a two layer preform (2.5″ OD, 0.625″ID) with Blend 1 on the ID and Blend 2 on the OD. The object ofpreforming is to compact the blends in size and to make a preform thatcan be inserted into an extrusion machine. The preform was placed intoan extrusion machine and extruded into tubing using a die and mandril.(0.2880″OD, 0.2650″ID) The tubing was run through a drying oven toremove the hydrocarbon lubricant. The tubing was then run through 3sintering ovens to cure the material. This tubing was then cut into8.25″ lengths.

[0086] The tubing produced has dimensions of 0.240″ OD×0.2170″ ID×8.25″long. The wall thickness is 0.0115″. The overall tube is two layers witha shiny white outside layer and a yellow inside layer. TABLE 4 SAMPLE 1PRESENT SAMPLE 2 SAMPLE 3 INVENTION UNDERCURE OVERCURE Drying oven 1 (F)400 400 400 Curing oven 1 (F) 820 720 1000 Curing oven 2 (F) 920 8201160 Curing oven 3 (F) 1000 920 1160 Melting Point (C) 325.96 343.33329.38 Tensile Strength 7000 1333 7400 (PSI) Elongation (%) 250 250 350Peel strength (lb) 1.56 0.4 >2.5* Peel Comments Straight, Straight, evenpeel. *Could not even peel Lots of stringers. peel.

[0087] Description of Samples:

[0088] Sample 1—This is an example of the present invention. This is apeelable product. This product is precision sintered. The peel strengthis typical for precision sintered product. The peel is straight and evenso that the entire tubing is split.

[0089] Sample 2—This sample is almost completely uncured product. Thisis visible by a melting peak at 344 degrees C versus 327 degrees C forthe other samples. This product is opaque, dull white due to theundercure. The peel is straight and even, however, there are significantnumbers of fibers that stick out of the peeled surface after beingpeeled. The peel strength is unacceptably low. This is unacceptable tothe end user since a piece may tear away and contaminate the area. Inaddition, the physical properties are significantly reduced due to thelack of curing of the product.

[0090] Sample 3—This product is fully cured. This makes a tube that isdimensionally stable, but cannot be peeled. The peel force increases togreater than 2.5 lb. and then the product tears. This product does notpeel evenly.

EXAMPLE 3

[0091] Tubing manufacturing: Blend 1—25 lb. of PTFE fine powder (Teflon®T6C, DuPont) was mixed with 4.5 lb. of a hydrocarbon lubricant (Isopar®G, Exxon) and 3.3 lb. of a radiopaque filler (67% Bi₂O₃ in Isopar G,Caloric) in a Patterson-Kelly V-cone blender. The materials were blendedfor 20 minutes. This mix was then allowed to age for several hours toequilibrate.

[0092] Blend 2—25 lb. of PTFE fine powder (Teflon®D T6C, DuPont) wasmixed with 5.1 lb. of a hydrocarbon lubricant (Isopar® G, Exxon) and 0.3lb. of a white pigment (67% white pigment in Isopar G, Caloric) in aPatterson-Kelly V-cone blender. The materials were blended for 20minutes. This mix was then allowed to age for several hours toequilibrate.

[0093] The two blends were then made into a two layer preform (2.5″ OD,0.625″ ID) with Blend 2 on the OD and Blend 1 on the ID. (The object ofpreforming is to compact the blends in size and to make a preform thatcan be inserted into an extrusion machine.) The preform was placed intoan extrusion machine and extruded into tubing. The tubing was runthrough a drying oven at approximately 400 degrees F to remove thehydrocarbon lubricant. The tubing was then run through sintering ovensat approximately 1000 degrees F to cure the material. This tubing wascut into 8.25″ lengths.

[0094] The tubing produced had dimensions of 0.144″ OD×0.125″ ID×8.25″in length with a wall thickness of 0.0095″. The outer 0.00475″ was Blend2 and the inner 0.00475″ was Blend 1. The overall tube had a white colorwith a yellow inside when cut apart.

[0095] Device manufacture: The tubing was then punched with two holes. Aslit was made between the two holes. Buttons were placed in the punchedholes and a hub was overmolded onto the tubing. The opposite end wasthen tipped using a Rf tipping machine and trimmed to size. The finishedsheath assembly was white in color with no visible discoloration. Thesheath assembly was then placed over a matching size dilator.

EXAMPLE 4

[0096] This example shows how additional heat added to a precisionsintered product renders it useless for peelable PTFE. The tableillustrates that precision sintered product can be taken out of theuseful range by the application of additional heat. It also shows thatskived product is not affected by the addition of additional heat. TABLE5 SAMPLE 1 SAMPLE 2 SAMPLE 3 Skived No No Yes Precision sintered Yes YesYes Post cured No Yes Yes Peel Strength (lb.) 1.63 2.93 1.26 PeelComments Straight, Uneven peel, Straight even peel partial peel evenpeel

[0097] Description of Samples:

[0098] Sample 1—Product from Example 1, Sample 2.

[0099] Sample 2—Product from Example 1, Sample 2 was taken and placed ina 700 degree F oven for 20 minutes. This product is no longer precisionsintered since it was post-sintered.

[0100] Sample 3—Product from Example 1, Sample 2 that was skived andthen placed in a 700 degree F oven for 20 minutes. This product is nolonger precision sintered since it was post-sintered.

COMPARATIVE EXAMPLE 1

[0101] The tubing was made identical to Example 3 except that instead ofusing Blend 2 on the OD, Blend 1 was used for the entire preform. Thus,one layer of tubing is produced that is Blend 1 throughout. Thisproduced tubing that was yellow in color.

[0102] The tubing was finished in the same manner as listed in Example3. The finished sheath assembly was yellow in color with brown and blackcolored spots in the tipped section. This is unacceptable for highquality product.

COMPARATIVE EXAMPLE 2

[0103] Blend 3 is a combination of Blend 1 and Blend 2—25 lb. of PTFEfine powder (Teflon® T6C, DuPont) was mixed with 4.4 lb. of ahydrocarbon lubricant (Isopar® G, Exxon), 3.3 lb. of a radiopaque filler(67% Bi₂O₃ in Isopar G, Caloric), and 0.3 lb. of a white pigment (67%white pigment in Isopar G, Caloric) in a Patterson-Kelly V-cone blender.The materials were blended for 20 minutes. This mix was then allowed toage for several hours to equilibrate.

[0104] The tubing was made identical as that described in ComparativeExample 1 except that instead of using Blend 2, Blend 3 was used. Thisproduced tubing that was white in color and radiopaque.

[0105] The tubing was finished in the same manner as described inExample 3. The finished sheath assembly was white in color with brownand black colored spots in the tipped section. This is unacceptable forhigh quality product.

[0106] The foregoing description of the present invention is merelyillustrative thereof, and it is understood that variations andmodification can be made without departing from the spirit or scope ofthe invention as set forth in the following examples and claims.

What is claimed is:
 1. A medical introducer device comprising: (a) a single-layer, peelable PTFE sheath having a bore extending therethrough and that does not include mechanically produced skiving for longitudinal splitting of the sheath, the sheath thermally cured to provide a peel strength of at least about 0.5 lbs with a standard deviation of no greater than about 0.40; and (b) a hub unit attached at a proximal end of the peelable sheath which facilitates splitting of the peelable sheath upon application of an effective shearing force thereon.
 2. The device of claim 1 wherein the sheath has a peel strength of at least about 0.70.
 3. The device of claim 1 wherein the sheath has a peel strength of at least about 1.0.
 4. The device of claim 1 wherein the sheath has a peel strength standard deviation of no more than about 0.30.
 5. The device of claim 1 wherein the sheath has a peel strength standard deviation of no more than about 0.20.
 6. The device of claim 1 further comprising a plurality of wing portions attached to the hub unit on opposing sides for grasping the hub unit.
 7. The device of claim 1 wherein the peelable sheath comprises a detectable material capable of external visualization.
 8. The device of claim 1 further comprising a needle or dilator assembly extending longitudinally within the bore of the peelable sheath
 9. A medical introducer device comprising: (a) a multi-layer, peelable PTFE sheath having a bore extending therethrough, and that does not include mechanically produced skiving for longitudinal splitting of the sheath, the sheath thermally cured to provide a peel strength of at least about 0.5 lbs with a standard deviation of no greater than about 0.40; and (b) a hub unit attached at a proximal end of the peelable sheath which facilitates splitting of the peelable sheath upon application of an effective shearing force thereon.
 10. The device of claim 9 wherein the sheath has a peel strength of at least about 0.70.
 11. The device of claim 9 wherein the sheath has a peel strength of at least about 1.0.
 12. The device of claim 9 wherein the sheath has a peel strength standard deviation of no more than about 0.30.
 13. The device of claim 9 wherein the sheath has a peel strength standard deviation of no more than about 0.20.
 14. The device of claim 9 further comprising a plurality of wing portions attached to the hub unit on opposing sides for grasping the hub unit.
 15. The device of claim 9 further comprising a needle or dilator assembly extending longitudinally within the bore of the peelable sheath
 16. The device of claim 9 wherein the multi-layer, peelable sheath comprises a thermally stable outer layer and at least one inner layer.
 17. The device of claim 16 wherein the inner layer comprises a detectable material capable of external visualization.
 18. The device of claim 16 wherein the thermally stable outer layer of the peelable sheath comprises a pigment.
 19. The device of claim 18 wherein the outer layer and inner layer of the peelable sheath each comprise visibly distinct pigments.
 20. A method of manufacturing a single-layer, peelable PTFE sheath that does not include mechanically produced skiving for longitudinal splitting of the sheath, the method comprising: (a) providing a PTFE preform material; (b) extruding the preform material into tubing; (c) drying the tubing; and (d) curing the tubing to provide a peel strength of at least about 0.5 lbs with a standard deviation of no greater than about 0.40.
 21. The method of claim 20 further comprising adding a detectable material to the preform blend in an amount sufficient to facilitate external visualization by X-ray or fluoroscopic procedures.
 22. The method of claim 20 further comprising: (a) affixing a hub unit onto a proximal end of the peelable sheath; (b) attaching a plurality of wing portions to opposing sides of the hub unit; and (c) tipping the peelable sheath at a distal end thereof.
 23. The method of claim 22 wherein the tipping comprises thermally treating the sheath.
 24. A method of manufacturing a multi-layer, PTFE peelable sheath that does not include mechanically produced skiving for longitudinal splitting of the sheath, comprising: (a) preparing a first preform PTFE material for forming the inner layer of the peelable sheath; (b) preparing a second preform PTFE material for forming the outer layer of the peelable sheath; (c) combining the first preform material and second preform material blend into a two layer preform; (d) extruding the two layer preform into tubing; (e) drying the tubing; and (f) curing the tubing using a precision sintering process.
 25. The method of claim 24 further comprising equilibrating the first preform material and second preform material prior to their combination.
 26. The method of claim 24 further comprising adding a detectable material to the first preform blend in an amount sufficient to facilitate external visualization.
 27. The method of claim 24 further comprising adding a colored pigment to at least one of the first preform material and the second preform material.
 28. The method of claim 24 further comprising: (a) affixing a hub unit onto a proximal end of the peelable sheath; (b) attaching a plurality of wing portions to opposing sides of the hub unit; and (c) tipping the peelable sheath at a distal end thereof.
 29. The method of claim 28 wherein tipping the peelable sheath comprises using a thermal process.
 30. A method of introducing a catheter or guide wire into a patient comprising: (a) providing a medical introducer device of claim 1; (b) piercing and dilating the vasculature of the patient using the needle or dilator assembly; (c) inserting the catheter or guidewire through the bore of the peelable sheath into vasculature of the patient; (d) applying cooperating forces to the wing portions of the hub unit to axially shear the peelable sheath; and (e) removing the peelable sheath from the vasculature of the patient.
 31. A method of introducing a catheter or guide wire into a patient comprising: (a) providing a medical introducer device of claim 9; (b) piercing and dilating the vasculature of the patient using the needle or dilator assembly; (c) inserting the catheter or guidewire through the bore of the peelable sheath into vasculature of the patient; (d) applying cooperating forces to the wing portions of the hub unit to axially shear the peelable sheath; and (e) removing the peelable sheath from the vasculature of the patient. 